The present invention relates to an image-pickup apparatus having an AF (auto focus) function such as a digital still camera and a video camera, specifically an image-pickup apparatus having a hybrid AF function capable of using plural AF methods in combination.
Focus control of video cameras is mainly performed by a so-called TV-AF (or a contrast AF method). The TV-AF method is a method in which an AF evaluation value signal is generated by extracting high frequency components from a video signal acquired by photoelectrical conversion of an object image by an image-pickup element and a focus lens is then moved such that the AF evaluation value increases to a maximum. The TV-AF method enables a high accurate focusing because an in-focus determination is done by using a video signal acquired by actually picking up an object image.
In addition, AF methods include an external ranging (distance measuring) method in which an exterior ranging sensor is used. In the external ranging method, a passive ranging method is performed by dividing a luminous flux from an object into two luminous fluxes and receiving them on two light-receiving sensors (line sensors) to calculate a correlation of signals from the line sensors. In the passive ranging method, a shift amount corresponding to the number of pixels of the line sensor at which the correlation reaches a maximum is calculated and ranging information is then acquired on the basis of the shift amount by the principal of triangulation.
On the other hand, active ranging methods include a method in which an ultrasonic sensor is used and ranging is performed by calculation from a propagation velocity of ultrasonic, and a method in which an infrared sensor is used and ranging is performed by triangulation.
These external ranging methods enable to rapidly acquire an in-focus state because an object distance is directly calculated.
Furthermore, AF methods include a TTL phase difference detection method that is often used in single-reflex cameras. The phase difference detection method is a method in which a luminous flux from an image-pickup optical system is divided into two luminous fluxes to cause them to form two images on light-receiving elements (line sensors). In the phase difference detection method, displacement amount (phase difference) and direction of the two images on the line sensors are detected to calculate drive amount and direction of a focus lens for acquiring an in-focus state and then the focus lens is driven.
A hybrid AF has been proposed which uses the above-mentioned external ranging method or phase difference detection method and the above-mentioned TV-AF method in combination (see Japanese Patent Laid-Open No. 2002-258147). In the hybrid AF, a focus lens is rapidly driven to the vicinity of an in-focus position by the external ranging method or the phase difference detection method and then the focus lens is accurately driven from that position to the in-focus position by the TV-AF method.
In addition, in an image-pickup apparatus having such a hybrid AF function, areas for ranging or focus detection (hereinafter the areas are also referred to as detection target areas) may be different in the respective AF methods. Japanese Patent Laid-Open No. 2002-311328 has disclosed an image-pickup apparatus which provides a focus target area and an in-focus determination result in the hybrid AF to a user with a display or sound when a shutter button is half-pressed in a still image pickup mode.
However, the image-pickup apparatus disclosed in Japanese Patent Laid-Open No. 2002-311328 has no function of indicating which one of the external ranging method or phase difference detection method and the TV-AF method is used in the current focus control. In other words, the image-pickup apparatus disclosed in Japanese Patent Laid-Open No. 2002-311328 merely provides focus target areas and in-focus determination results in these AF methods. Therefore, it is difficult to confirm whether or not operations of the hybrid AF in which focus control by the TV-AF method is performed after focus control by the external ranging method or phase difference detection method is performed are normally performed.
Furthermore, as described above, in the hybrid AF the detection target areas may be different in the respective AF methods combined with each other. In particular, a hybrid AF which uses the TV-AF method and the external ranging method in combination causes, as shown in FIG. 9, a parallax between a focus detection area A1 for the TV-AF method and a ranging area A2 for the external ranging method. This is because an external ranging sensor 302 is provided at a position displaced upward with respect to an optical axis (image-pickup optical axis) of a lens unit 301.
In the case where the external ranging sensor 302 is provided at a position displaced with respect to the image-pickup optical axis, the center C1 of the focus detection area A1 coincides with the center C2 of the ranging area A2 at a certain object distance D2. In this case, focus controls by the TV-AF method and the external ranging method are performed for the same object.
However, the center C2 of the ranging area A2 is displaced vertically from the center C1 of the focus detection area A1 at farther and nearer object distances D1 and D3 than the object distance D2. Accordingly, an in-focus target object in the external ranging method differs from an original in-focus target object (that is, an object intended by a user) in the TV-AF method.
In such a case where the focus control by the external ranging method is performed for an object that is different from the original in-focus target object, the image-pickup apparatus having no function of indicating that the focus control by the external ranging method is currently performed may cause the user to feel that something is wrong in the video camera.